1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more specifically, to a method for forming metal wires in a semiconductor device.
2. Discussion of Related Art
As a semiconductor memory device is highly integrated, metal wires are multi-layered. The operating speed of the device is greatly influenced by RC delay among the metal wires. RC delay refers to a signal transfer delay phenomenon caused by parasitic capacitance (C) between the metal wires and an insulating film. The amount of RC delay depends on specific resistance of the metal wires and the dielectric constant of the insulating film between the wires. Therefore, if the metal wires are formed using a material of low specific resistance and the insulating film between the wires is formed using a material of a low dielectric constant, RC delay can be reduced.
In order to reduce RC delay, a method in which the metal wires are formed using a Cu film and the insulating film between the wires is formed using a porous dielectric film has been employed. The Cu wire is usually formed by means of the damascene process. The damascene process includes filling a wiring region defined in the insulating film between the wires with a metal film such as the Cu film.
Meanwhile, before the Cu film is formed, an anti-diffusion film is formed in order to prevent diffusion of Cu. If the anti-diffusion film is formed on the porous dielectric film, however, the anti-diffusion film is not continuously connected but broken or thinly formed due to pores exposed on the surface of the porous dielectric film. Accordingly, there occurs a problem that the properties of the anti-diffusion film formed on the porous dielectric film are degraded. That is, the anti-diffusion film formed defectively does not effectively prevent Cu within the Cu wire from being diffused into the porous dielectric film. Moreover, if bias thermal stress (BTS) is applied to the Cu wire, Cu can more easily slip toward the sidewall of the porous dielectric film, resulting in fail. In other words, as shown in FIG. 1, if the Cu wire is formed in the wiring region defined in the porous dielectric film by means of the damascene process and BTS is applied to the Cu wire, Cu is diffused and fail is thus generated.